Financial Instruments - Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Mar. 28, 2020	Sep. 28, 2019
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 194,759	$ 204,977
Unrealized Gains	1,008	1,202
Unrealized Losses	(2,923)	(281)
Fair Value	192,844	205,898
Cash and Cash Equivalents	40,174	48,844
Current Marketable Securities	53,877	51,713
Non-Current Marketable Securities	98,793	105,341
Total cash, cash equivalents and marketable securities that were restricted from general use	17,600	18,900
Marketable securities pledged as collateral under repurchase agreements	2,600
Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	4,473	15,897
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	4,473	15,897
Cash and Cash Equivalents	4,473	15,897
Current Marketable Securities	0	0
Non-Current Marketable Securities	0	0
Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	165,881	176,876
Unrealized Gains	1,008	1,202
Unrealized Losses	(2,923)	(281)
Fair Value	163,966	177,797
Cash and Cash Equivalents	11,296	20,743
Current Marketable Securities	53,877	51,713
Non-Current Marketable Securities	98,793	105,341
Cash
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	24,405	12,204
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	24,405	12,204
Cash and Cash Equivalents	24,405	12,204
Current Marketable Securities	0	0
Non-Current Marketable Securities	0	0
Money market funds \| Level 1
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	4,473	15,897
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	4,473	15,897
Cash and Cash Equivalents	4,473	15,897
Current Marketable Securities	0	0
Non-Current Marketable Securities	0	0
U.S. Treasury securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	18,755	30,293
Unrealized Gains	405	33
Unrealized Losses	0	(62)
Fair Value	19,160	30,264
Cash and Cash Equivalents	1,042	6,165
Current Marketable Securities	6,736	9,817
Non-Current Marketable Securities	11,382	14,282
U.S. agency securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	6,079	9,767
Unrealized Gains	12	1
Unrealized Losses	(9)	(3)
Fair Value	6,082	9,765
Cash and Cash Equivalents	129	6,489
Current Marketable Securities	1,478	2,249
Non-Current Marketable Securities	4,475	1,027
Non-U.S. government securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	18,548	19,821
Unrealized Gains	97	337
Unrealized Losses	(693)	(50)
Fair Value	17,952	20,108
Cash and Cash Equivalents	652	749
Current Marketable Securities	2,348	3,168
Non-Current Marketable Securities	14,952	16,191
Certificates of deposit and time deposits \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	10,616	4,041
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	10,616	4,041
Cash and Cash Equivalents	3,661	2,024
Current Marketable Securities	6,319	1,922
Non-Current Marketable Securities	636	95
Commercial paper \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	15,690	12,433
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	15,690	12,433
Cash and Cash Equivalents	5,653	5,193
Current Marketable Securities	10,037	7,240
Non-Current Marketable Securities	0	0
Corporate debt securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	82,153	85,383
Unrealized Gains	207	756
Unrealized Losses	(2,177)	(92)
Fair Value	80,183	86,047
Cash and Cash Equivalents	159	123
Current Marketable Securities	25,708	26,127
Non-Current Marketable Securities	54,316	59,797
Municipal securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	974	958
Unrealized Gains	9	8
Unrealized Losses	(1)	(1)
Fair Value	982	965
Cash and Cash Equivalents	0	0
Current Marketable Securities	53	68
Non-Current Marketable Securities	929	897
Mortgage- and asset-backed securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	13,066	14,180
Unrealized Gains	278	67
Unrealized Losses	(43)	(73)
Fair Value	13,301	14,174
Cash and Cash Equivalents	0	0
Current Marketable Securities	1,198	1,122
Non-Current Marketable Securities	$ 12,103	$ 13,052

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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